Junction flows

Junction hows occur when a boundary layer encounters an obstacle attached t o the same surface. Physical phenomena that have been observed for blunt an d streamlined obstacles are discussed for both laminar and turbulent approa ching boundary layers. The pressure gradients around an obstacle produce a three-dimensional separation with horseshoe vortices that wrap around the o bstacle. Except for very low Reynolds number laminar flows, these vortices are highly unsteady and are responsible for high turbulence intensities, hi gh surface pressure fluctuations and heat transfer rates, and erosion scour in the nose region of the obstacle. Calculation methods are also reviewed; methods that capture the large-scale chaotic vortical motions should be us ed for computations. Some work on the control, modification, or elimination of such vortices is also reviewed.